Method for using a base station to selectively utilize B and D channels to support a plurality of communications

ABSTRACT

A method for using a wireless digital base station to receive, process and transmit a plurality of communications having independent data rates establishing a first communication channel having a first data communication rate to support a first communication; determining the data rate required to support the first communication; selecting one or more transmission channels, from a plurality of available transmission channels, required to support said required data rate; and transmitting the first communication using one or more selected transmission channels. The plurality of available transmission channels includes at least one B or D channel.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.10/810,007, filed Mar. 26, 2004, which is a continuation of U.S. patentapplication Ser. No. 10/080,835 filed Feb. 22, 2002, which issued asU.S. Pat. No. 6,798,759 on Sep. 28, 2004, which is a continuation ofU.S. patent application Ser. No. 09/591,611 filed Jun. 9, 2000, whichissued as U.S. Pat. No. 6,373,830 on Apr. 16, 2002, which is acontinuation of application Ser. No. 08/898,537, filed Jul. 22, 1997,which issued as U.S. Pat. No. 6,075,792 on Jun. 13, 2000, which in turnclaims priority from U.S. provisional application no. 60/049,637 filedon Jun. 16, 1997, which are incorporated by reference as if fully setforth.

FIELD OF INVENTION

This invention generally relates to wireless communication systems. Moreparticularly, the invention relates to a wireless digital Code DivisionMultiple Access (CDMA) communication system including a base station anda plurality of subscriber units which selectively allocates bandwidthupon demand by a subscriber unit or an entity desiring to establish acommunication with a subscriber unit.

BACKGROUND

The use of wireless technology by the telecommunication industry hasincreased dramatically as the capacity and reliability of wirelesscommunication systems has improved. Once considered only to be aconvenient method for sending voiced communications, digital wirelesscommunications systems are now a necessity for providing transmission ofall forms of communications including plain old telephony service(POTS), integrated services digital network (ISDN), variable bit rate(VBR) data service, wideband service, leased line service and packetdata services. Although it has been technically feasible to transmit allof these types of services, the large amount of bandwidth required forhigh data rate communications has made many of these servicesuneconomical. As the number of subscribers requiring access to wirelessdigital communication systems has increased, the reliance on a widebandwidth for each communication is no longer realistic.

The finite bandwidth allocated to wireless communications systems forpublic use has become increasingly valuable. Since it is unlikely thatadditional bandwidth to support user growth will be allocated forexisting applications, many of the recent advances in telecommunicationhardware and software have been directed toward increasing thetransmission rate of data while utilizing a decreased amount ofbandwidth.

Accordingly, there exists a need for a wireless digital communicationsystem which supports the same high data rate services as conventionalwired networks while utilizing the allocated bandwidth more efficiently.

SUMMARY

The present invention is a CDMA wireless digital communication systemwhich supports all types of voice and data communications whileutilizing the minimum amount of bandwidth for the particularapplication. The system efficiently allocates ISDN bandwidth on demandby a subscriber. Upon initialization of the subscriber unit, the systemestablishes a channel and generates the necessary spreading codes tosupport the highest capacity channel desired by the subscriber unit.However, the system does not set aside portions of the communicationbandwidth until actually required by the subscriber unit. Since the callsetup is performed at the beginning of any call from that particularsubscriber unit, including the assignment of spreading codes, asubscriber unit can quickly gain access to the portion of the spectrumthat is required to support the particular application.

Accordingly, it is an object of the invention to provide a wirelessdigital spread spectrum communication system which supports a range oftelephone services including POTS and ISDN while efficiently utilizingthe spread spectrum bandwidth.

Other objects and advantages of the present invention will becomeapparent after reading the description of a presently preferredembodiment.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a block diagram of a code division multiple access spreadspectrum communication system according to the present invention;

FIG. 2A is a block diagram of the interface between the subscriber unitof the present invention and an ISDN terminal;

FIG. 2B is a block diagram of the interface between the subscriber unitof the present invention and a POTS terminal;

FIG. 2C is a block diagram of the interface between the subscriber unitof the present invention and a packet terminal;

FIG. 2D is a block diagram of the interface between the subscriber unitof the present invention and a wideband connection;

FIG. 2E is a block diagram of the interface between the subscriber unitof the present invention and a leased line terminal;

FIG. 2F is a block diagram of the interface between the subscriber unitof the present invention and an ISDN and POTS network;

FIG. 2G is a block diagram of the interface between the subscriber unitof the present invention and a wideband and packet network;

FIG. 2H is a block diagram of the interface between the subscriber unitof the present invention and a leased line network;

FIG. 3 is a block diagram of a subscriber unit in accordance with thepresent invention;

FIG. 4 is a block diagram of an RCS in accordance with the presentinvention;

FIG. 5 is a flow diagram of the procedure for dynamic allocation ofbandwidth for ISDN service;

FIGS. 6A and 6B are flow diagrams of the establishment of the bearerchannel between the subscriber unit and the RCS for POTS service;

FIG. 7 shows the layered protocol of the communications between thesubscriber unit and RCS;

FIG. 8A illustrates the simplified bearer switching method as initiatedby the subscriber unit;

FIG. 8B illustrates the simplified bearer switching method as initiatedby the RCS; and

FIGS. 9A and 9B are flow diagrams of the establishment of the bearerchannel between the subscriber unit and the RCS for ISDN service.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The preferred embodiment will be described with reference to the drawingfigures wherein like numerals represent like elements throughout.

The system of the present invention provides local-loop telephoneservice using radio links between one or more base stations and at leastone remote subscriber unit. In the exemplary embodiment, the radio linkis described for a base station communicating with a fixed subscriberunit (FSU), but the system is equally applicable to systems includingmultiple base stations with radio links to both fixed subscriber unitsand mobile subscriber units (MSUs). Consequently, the fixed and mobilesubscriber units will be referred to herein as subscriber units.

Referring to FIG. 1, a base station 101 provides call connection to alocal exchange 103 or any other telephone network switching interface,such as a private branch exchange (PBX), and includes at least one radiocarrier station (RCS) 104, 105 . . . 110. One or more RCSs 104, 105, 110connect to a radio distribution unit (RDU) 102 through links 131, 132,137, 138, 139 and RDU 102 interfaces with the local exchange 103 bytransmitting and receiving call set-up, control, and information signalthrough telco links 141, 142, 150. The subscriber units 116, 119communicate with the RCS 104 through radio links 161, 162, 163, 164,165. Alternatively, another embodiment of the invention includes severalsubscriber units and a “master subscriber unit” with functionalitysimilar to the RCS 104. Such an embodiment may or may not haveconnection to a local telephone network.

The radio links 161 to 165 operate within the frequency bands of theCDS1800 standard (1.71-1.785 GHz and 1.805-1.880 GHz); the US-PCSstandard (1.85-1.99 GHz); and the CEPT standard (2.0-2.7 GHz). Althoughthese bands are used in the described embodiment, the invention isequally applicable to any RF frequency band including the entire UHF andSHF bands, and bands from 2.7 GHz to 5 GHz. The transmit and receivebandwidths are multiples of 3.5 MHz starting at 7 MHz, and multiples of5 MHz starting at 10 MHz, respectively. The described system includesbandwidths of 7, 10, 10.5, 14 and 15 MHz. In the exemplary embodiment ofthe invention, the minimum guard band between the uplink and downlink is20 MHz, and is desirably at least three times the signal bandwidth. Theduplex separation is between 50 to 175 MHz, with the described inventionusing 50, 75, 80, 95 and 175 MHz. Other frequencies may also be used.

Although the system may use different spread-spectrum bandwidthscentered around a carrier for the transmit and receive spread-spectrumchannels, the present invention is readily extended to systems usingmultiple spread-spectrum bandwidths for the transmit channels andmultiple spread-spectrum bandwidths for the receive channels.Alternatively, the same spread-spectrum bandwidth for both the transmitand receive channels may be employed wherein uplink and downlinktransmissions will occupy the same frequency band. The present inventionmay also be readily extended to multiple CDMA frequency bands, eachconveying a respectively different set of messages, uplink, downlink oruplink and downlink.

The spread binary symbol information is transmitted over the radio links161 to 165 using quadrature phase shift keying (QPSK) modulation withNyquist pulse shaping. However, other modulation techniques may be usedincluding, but not limited to, offset QPSK minimum shift keying (MSK),Gaussian phase shift keying (GPSK) and M-ary phase shift keying (MPSK).

The radio links 161 to 165 incorporate broadband code division multipleaccess (B-CDMA™) technology as the mode of transmission in both theuplink and downlink directions. CDMA (also known as spread spectrum)communication techniques used in multiple access systems are well-known,and are described in U.S. Pat. No. 5,228,056 entitled SYNCHRONOUSSPREAD-SPECTRUM COMMUNICATION SYSTEM AND METHOD by Donald Schilling. Thesystem described utilizes the direct sequence spreading technique. TheCDMA modulator generates the spread-spectrum spreading code sequence,which can be a pseudonoise sequence, and performs complex directsequence modulation of the QPSK signals with spreading code sequencesfor the In-phase (I) and Quadrature (Q) channels. Pilot signals,spreading codes which are not modulated by data, are generated andtransmitted with the modulated signals. The pilot signals are used forsynchronization, carrier phase recovery, and for estimating the impulseresponse of the radio channel. Each subscriber unit 111-118 includes acode generator and at least one CDMA modulator and demodulator, whichtogether comprise a CDMA modem. Each RCS 104, 105, 110 has at least onecode generator plus sufficient CDMA modulators and demodulators for allof the logical channels in use by the subscriber units.

The CDMA demodulator despreads the signal with appropriate processing toreduce or exploit multipath propagation effects. The radio links supportmultiple traffic channels with data rates of 8, 16, 32, 64, 128 and 144kb/s. The physical channel to which a traffic channel is connectedoperates with a 64 k symbol/sec rate. Other data rates may be supported,and forward error correction (FEC) coding can be employed. For thedescribed embodiment, FEC with a coding rate of 1/2and a constraintlength 7 is used. Other rates and constraint lengths can be usedconsistent with the code generation techniques employed.

Referring again to FIG. 1, the RCS 104 interfaces to the RDU 102 througha plurality of RF links or terrestrial links 131, 132, 137 with, forexample, 1.533 Mb/s DS1, 2.048 Mbs/E1; or HDSL formats to receive andsend digital data signals. While these are typical telephone companystandardized interfaces, the present invention is not limited to thesedigital data formats only. The exemplary RCS line interface (not shownin FIG. 1) translates the line coding (such as HDB3, B8ZS, AMI) andextracts or produces framing information, performs alarms and facilitysignaling functions, as well as channel specific loop-back and paritycheck functions. This provides 64 kb/s PCM encoded or 32 kb/s ADPCMencoded telephone traffic channels or ISDN channels to the RCS 104, 105,110 for processing as will be described in greater detail hereinafter.Other voice compression techniques can be used consistent with thesequence generation techniques.

The system of the present invention also supports bearer ratemodification between the RCS 104 and the subscriber unit 111 for bothPOTS service and ISDN service. The subscriber units 111-118 mayinterface with a telephone unit 170, a local switch (PBX) 171, a dataterminal 172, an ISDN interface 173 or other types of equipment shown inFIGS. 2A-2H. The input from the telephone unit 170 may include voice,voiceband data and signaling. Although the present invention isapplicable to the communications between a plurality of subscriber units111-118 and a plurality of RCSs 104-110, reference hereinafter will bemade to a particular subscriber unit and RCS for simplicity. If thesignals input into the subscriber unit are not digital, the subscriberunit 111 translates the analog signals into digital sequences fortransmission to the RCS 104. The subscriber unit 112 encodes voice datawith techniques such as ADPCM at rates of 32 kb/s or lower. The RCS 104detects voiceband data or facsimile data with rates above 4.8 kb/s tomodify the bearer rate of the traffic channel for unencodedtransmission. Also A-law, u-law, or no companding of the signal may beperformed before transmission. As is well known to those of skill in theart, data compression techniques for digital data such as idle flagremoval may also be used to conserve capacity and minimize interference.

The system of the present invention also supports bearer ratemodification between the RCS 104 and the subscriber unit 111 for bothPOTS service and ISDN service. The subscriber units 111-118 mayinterface with a telephone unit 170, a local switch (PBX) 171, a dataterminal 172, an ISDN interface 173 or other types of equipment shown inFIGS. 2A-2H. The input from the telephone unit 170 may include voice,voiceband data and signaling. Although the present invention isapplicable to the communications between a plurality of subscriber units111-118 and a plurality of RCSs 104-110, reference hereinafter will bemade to a particular subscriber unit and RCS for simplicity. If thesignals input into the subscriber unit are not digital, the subscriberunit 111 translates the analog signals into digital sequences fortransmission to the RCS 104. The subscriber unit 112 encodes voice datawith techniques such as ADPCM at rates of 32 kb/s or lower. The RCS 104detects voiceband data or facsimile data with rates above 4.8 kb/s tomodify the bearer rate of the traffic channel for unencodedtransmission. Also A-law, u-law, or no companding of the signal may beperformed before transmission. As is well known to those of skill in theart, data compression techniques for digital data such as idle flagremoval may also be used to conserve capacity and minimize interference.

The transmit power level of the radio interface between the RCS 104 andthe subscriber unit 111 is controlled using a different closed looppower control method for the downlink and uplink directions. Theautomatic forward power control (AFPC) method determines the downlinktransmit power level and the automatic reverse power control (ARPC)method determines the uplink transmit power level. The logical controlchannel by which the subscriber unit 111 and the RCS 104 transfer powercontrol information operates at an update rate of at least a 16 kHz.Other embodiments may use a faster or slower update rate, for example 64kHz. These algorithms ensure that the transmit power of a user maintainsan acceptable bit-error rate (BER), maintain the system power at aminimum to conserve power and maintain the power level of the subscriberunit 111 as received by the RCS 104 at a nearly equal level.

The system also uses an optional maintenance power control method duringthe inactive mode of the subscriber unit 111. When the subscriber unit111 is inactive or powered-down to conserve power, the subscriber unit111 occasionally activates to adjust its initial transmit power levelsetting in response to a maintenance power control signal from the RCS104. The maintenance power control signal is determined by the RCS 104by measuring the received power level of the subscriber unit 111 andpresent system power level and calculating the necessary initialtransmit power. The method shortens the channel acquisition time of thesubscriber unit 111 to begin a communication and prevents the transmitpower level of the subscriber unit 111 from becoming too high andinterfering with other channels during the initial transmission beforethe closed loop power control reduces the transmit power.

The RCS 104 obtains synchronization of its clock from an interface linesuch as, but not limited to, E1, T1, or HDSL interfaces. The RCS 104 canalso generate its own internal clock signal from an oscillator which maybe regulated by a global positioning system (GPS) receiver. The RCS 104generates a global pilot code, which can be acquired by the remotesubscriber unit 111. All transmission channels of the RCS 104 aresynchronized to the global pilot channel. The spreading code phases ofcode generators (not shown in FIG. 1) used for logical communicationchannels within the RCS 104 are also synchronized to the spreading codephase of the global pilot channel. Similarly, all subscriber units111-118 which receive the global pilot code of the RCS 104 synchronizethe spreading and de-spreading code phases of their code generators tothe global pilot code.

Typically, a prior art channel is regarded as a communications pathwhich is part of an interface and which can be distinguished from otherpaths of that interface without regard to its content. However, for CDMAcommunications, separate communications paths are distinguished by theircontent. All logical channels and subchannels of the present inventionare mapped to a common 64 kilo-symbols per second (ksym/s) QPSK stream.Some channels are synchronized to associated pilot codes which aregenerated from, and perform a similar function to, the global pilotcode. The system pilot signals are not considered logical channels.

Several logical communication channels are used over the RFcommunication link between the RCS 104 and the subscriber unit 111. Eachlogical communication channel either has a fixed, pre-determinedspreading code or a dynamically assigned spreading code. For bothpredetermined and assigned codes, the code phase is synchronized withthe global pilot code.

The spreading codes are specified by the seeds used to generate thecodes. A pool of “primary seeds” exists within the RDU 102, a portion ofwhich comprise global primary seeds and the remainder comprise assignedprimary seeds. The RDU 102 allocates these primary seeds to the RCSs 104on an as-needed basis. A global primary seed generates all of the globalchannel codes for use by an RCS 104 within a cell. However, assignedprimary seeds are used to generate secondary assigned seeds. One primaryassigned seed generates fifty-seven (57) secondary assigned seeds. Eachsecondary assigned seed is input into the code generators within the RCS104 and the subscriber unit 111 to generate a set of assigned channelcodes to support each communication link. In the preferred embodiment,each RCS 104 is given one global primary seed for generating globalchannel codes and two primary assigned seeds. Accordingly, the RCS 104and its corresponding subscriber units 111-118 may generate up to 114secondary assigned seeds. Each secondary assigned seed is assigned bythe RCS 104 to generate the codes for an active link, thereby permittingenough codes for up to 114 simultaneous communication links.

Logical communication channels are divided into two groups: 1) globalchannels; and 2) assigned channels. The global channel group includeschannels which are either transmitted from the RCS 104 to all subscriberunits 111-118 or from any subscriber unit 111-118 to the RCS 104regardless of the identity of the subscriber unit 111-118. Channels inthe assigned channels group are those channels dedicated tocommunication between the RCS 104 and a particular subscriber unit 111.

With respect to the global channel group, the global channel groupprovides for: 1) broadcast control logical channels, which providepoint-to-multi-point services for broadcasting messages to allsubscriber units 111-118 and paging messages to subscriber units111-118; and 2) access control logical channels which providepoint-to-point services on global channels for subscriber units 111-118to access the system and obtain assigned channels. The RCS 104 of thepresent invention has one broadcast control logical channel and multipleaccess control logical channels. A subscriber unit 111-118 of thepresent invention has at least one broadcast control logical channel andat least one access control logical channel.

The global logical channels controlled by the RCS 104 are the fastbroadcast channel (FBCCH) which broadcasts fast changing informationconcerning which services and which access channels are currentlyavailable, and the slow broadcast channel (SBCCH) which broadcasts slowchanging system information and paging messages.

The subscriber unit 111 uses an access channel (AXCH) to begincommunications with the RCS 104 and gain access to assigned channels.Each AXCH is paired with a control channel (CTCH) which is sent from theRCS 104 to the subscriber unit 111. The CTCH is used by the RCS 104 toacknowledge and reply to access attempts by the subscriber unit 111. Theshort access pilot (SAXPT) and the long access pilot (LAXPT) aretransmitted synchronously with AXCH to initiate access and to providethe RCS 104 with a time and phase reference. The SAXPT is transmitted bythe subscriber unit 111 while it ramps up its transmit power to initiateaccess to the RCS 104. Since the SAXPT is a relatively short code itpermits the RCS 104 to detect the subscriber unit 111 quickly and avoidspower overshoot by the subscriber unit 111. Further detail regardingtransmit power ramp-up using the SAXPT is described in more detail in anapplication entitled A METHOD OF CONTROLLING INITIAL POWER RAMP-UP INCDMA SYSTEMS BY USING SHORT CODES, Ser. No. 08/670,162; filed Jun. 27,1996 which is herein incorporated by reference as if fully set forth.Until the SAXPT is detected by the RCS 104, subscriber unit 111 does notsend any other signal. Once the SAXPT is detected, the subscriber unit111 starts transmitting the LAXPT which provides the RCS 104 with a timeand phase reference and permits the RCS 104 to determine the channelimpulse response.

With respect to the assigned channel group, this group contains thelogical channels that control a single communication link between theRCS 104 and the subscriber unit 111. When an assigned channel group isformed, a pair of power control logical message channels for each of theuplink and downlink connections is established and one or more pairs oftraffic channels, depending on the type of connection, is established.The bearer control function performs the required forward error control,bearer rate modification and encryption functions.

Each subscriber unit 111-118 has at least one assigned channel groupwhen a communication link is established, and each RCS 104-110 hasmultiple assigned channel groups, one for each communication link inprogress. An assigned channel group of logical channels is created for acommunication link upon successful establishment of the communicationlink. The assigned channel group includes encryption, FEC coding, andmultiplexing on transmission, and decryption, FEC decoding anddemultiplexing on reception.

Each assigned channel group provides a set of communication linkoriented point-to-point services and operates in both directions betweena specific RCS 104 and a specific subscriber unit 111. An assignedchannel group formed for a communication link can control more than onebearer over the RF communication channel associated with a singlecommunication link. Multiple bearers are used to carry distributed datasuch as, but not limited to, ISDN. An assigned channel group can providefor the duplication of traffic channels to facilitate switchover to 64kb/s PCM for high speed facsimile and modem services for the bearer ratemodification function.

The assigned logical channels formed upon a successful communicationlink and included in the assigned channel group are dedicated signalingchannel order wire (OW), APC channel and one or more traffic channels(TRCH) which are bearers of 8, 16, 32, or 64 kb/s depending on theservice supported. For voice traffic, moderate rate coded speech ADPCMor PCM can be supported on the traffic channels. For ISDN service types,two 64 kb/s TRCHs form the B channels and one 16 kb/s TRCH forms the Dchannel. Alternatively, the APC subchannel may either be separatelymodulated on its own CDMA channel, or may be time division multiplexedwith a traffic channel or OW channel.

Each subscriber unit 111-118 of the present invention supports up tothree simultaneous traffic channels. A subscriber unit is preferablycommissioned to be a POTS subscriber unit 112 or an ISDN subscriber unit115. Although POTS subscriber unit 112 does not support ISDN service inaccordance with the present invention, bandwidth resources can bedynamically allocated for either service type. For example, a POTSsubscriber unit 112 can set up an additional POTS line and tear it down,or an ISDN subscriber unit 115 can dynamically add B channel-carryingbearers or tear them down. For dynamic bandwidth allocation of a POTSservice, an active 32 kb/s ADPCM service modifies the bearer type from32 kb/s to 64 kb/s unencoded data to support facsimile transmission. Thepresence of a facsimile call is determined by the RCS 104 by monitoringthe existence of the 2100 Hz answer tone.

For dynamic bandwidth allocation of ISDN service, the RCS 104 monitorsthe ISDN D channel messages to determine when a B channel is requestedand when it should be torn down. Once the RCS 104 determines the needfor changing the bearer channel allocation, the RCS 104 initiates thedynamic bearer allocation procedure which will be described in greaterdetail hereinafter. The mapping of the three logical channels for TRCHsto the user data is shown below in Table 1:

TABLE 1 Mapping of service types to the three available TRCH channelsService TRCH(0) TRCH(1) TRCH(2) 16 kb/s POTS TRCH/16 not used not used32 + 64 kb/s POTS(during BCM) TRCH/32 TRCH/64 not used 32 kb/s POTSTRCH/32 not used not used 64 kb/s POTS not used TRCH/64 not used ISDN Dnot used not used TRCH/16 Digital LL @64 kb/s TRCH/64 not used not usedDigital LL @ 2 × 64 kb/s TRCH/64 TRCH/64 not used Analog LL @ 64 kb/sTRCH/64 not used not used

A subscriber unit 200 made in accordance with the present invention isgenerally shown in FIG. 3. The subscriber unit 200 includes a receiversection 202 and a transmitter section 204. An antenna 206 receives asignal from RCS 104, which is filtered by a band-pass filter 208 havinga bandwidth equal to twice the chip rate and a center frequency equal tothe center frequency of the spread spectrum system's bandwidth. Theoutput of the filter 208 is down-converted by a mixer 210 to a basebandsignal using a constant frequency (Fc) local oscillator. The output ofthe mixer 210 is then spread spectrum decoded by applying a PN sequencefor each logical channel to a mixer 212 within the PN Rx generator 214.The output of the mixer 212 is input to a codec 218 which interfaceswith the communicating entity 220.

A baseband signal from the communicating entity 220, for example theequipment shown in FIGS. 2A-2H, is pulse code modulated by the codec218. Preferably, a 32 kb/s adaptive pulse code modulation (ADPCM) isused. The PCM signal is applied to a mixer 222 within a PN Tx generator224. The mixer 222 multiplies the PCM data signal with the PN sequencefor each logical channel. The output of the mixer 222 is applied tolow-pass filter 226 whose cutoff frequency is equal to the system chiprate. The output of the filter 226 is then applied to a mixer 228 andsuitably up-converted, as determined by the carrier frequency Fc appliedto the other terminal. The up-converted signal is then passed through aband-pass filter 230 and to a broadband RF amplifier 232 which drives anantenna 234. Although two antennas 206, 234 are shown, the preferredembodiment includes a diplexer and a single antenna for transmission andreception. The digital signal processor (DSP) 236 controls theacquisition process as well as the Rx and Tx PN generators 214, 224.

The base station 101, which includes a plurality of RCSs 104, 105, 110made in accordance with the present invention is shown in FIG. 4. Forsimplicity, only one RCS 104 is shown. The base station 101 includes areceiver section 302 and a transmitter section 304. An antenna 306receives a signal from the subscriber unit, which is filtered by aband-pass filter 308 having a bandwidth equal to twice the chip rate anda center frequency equal to the center frequency of the spread spectrumsystem's bandwidth. The output of the filter 308 is down-converted by amixer 310 to a baseband signal using a constant frequency (Fc) localoscillator. The output of the mixer 310 is then spread spectrum decodedat each modem by applying a PN sequence to a mixer 312 within the PN Rxgenerator 314. The output of the mixer 316 is then forwarded to the RDU318.

A baseband signal is received from the RDU 318. Preferably, a 32 kb/sADPCM signal is used. The ADPCM or PCM signal is applied to a mixer 322within a PN Tx generator 324. The mixer 322 multiplies the ADPCM or PCMdata signal with the PN sequence. The output of the mixer 322 is appliedto low-pass filter 326 whose cutoff frequency is equal to the systemchip rate. The output of the filter 326 is then applied to a mixer 328and suitably up-converted, as determined by the carrier frequency Fcapplied to the other terminal. The up-converted signal is then passedthrough a band-pass filter 330 and to a broadband RF amplifier 332 whichdrives an antenna 334. Although two antennas 306, 334 are shown, thepreferred embodiment includes a diplexer and only one antenna fortransmission and reception. The digital signal processor (DSP) 336controls the acquisition process as well as the Rx and Tx PN generators314, 324.

The system provides a wireless link between the RCS 104 and theplurality of subscriber units 111-118. In order to conserve as muchbandwidth as possible, the system selectively allots the bandwidthrequired for supporting the data transmission rate required byparticular communication. In this manner, the system ensures that thebandwidth is utilized efficiently. For example, referring back to Table1, voiced communications may be effectively transmitted across a 32 kb/sadaptive pulse code modulation (ADPCM) channel. However, a high speedfacsimile or data modem signal requires at least a 64 k/bs PCM signal toreliably transmit the communication. Additionally, although a subscriberunit 115 has paid for ISDN service, which includes two 64 kb/s Bchannels and one 16 kb/s channel, the entire ISDN capacity is rarelyutilized at all times. Many different data transmission rates may alsobe utilized by originating and terminating nodes.

The originating and terminating nodes may comprise computers, facsimilemachines, automatic calling and answering equipment, data networks orany combination of this equipment. For robust communication of data itis imperative to ensure that the communication system switches to thedata transmission rate required by the communicating nodes prior to thetransmission of any data. The system must be able to effectivelyallocate bandwidth and dynamically switch between these datacommunication rates on demand by the user. Modification of thetransmission rate from a low rate (that supports voice communication) toa high rate (that supports encoded data communication) ensures that datawill be reliably and quickly transmitted over a communication channel.Additionally, if an ISDN D channel is presently allocated and one or twoB channels are required, the system must ensure that the code generatorsare activated in order to support the communication.

For POTS, there are two basic scenarios where the bearer channel (TRCHchannel) is either modified or a new bearer channel is added or torndown. First, the bearer channel is modified from 32 kb/s coded ADPCMtype to 64 kb/s uncoded PCM service to support a facsimile transmission.Second, a new bearer channel is added or torn down when the subscribergoes off hook while an OA&M (overhead, administration and maintenance)call is in progress, or when an OA&M call is initiated while a POTS callis in progress. While an OA&M silent call is in progress, the subscriberunit 112 can determine that the user is initiating a new POTS call bymonitoring the changes at the A/B interface between the subscriber unit112 and the communication equipment 170 (on-hook/off-hook sensor). Moredetail regarding the dynamic allocation of bandwidth for POTS may befound in an application entitled CODE DIVISION MULTIPLE ACCESS (CDMA)COMMUNICATION SYSTEM, patent application Ser. No. 08/815,299, filed Mar.11, 1997, which is a continuation-in-part of Ser. No. 08/669,775, filedJun. 27, 1996 by Lomp et al., which is incorporated herein by referenceas if fully set forth.

For ISDN service, the dynamic bandwidth allocation refers to selectiveallocation of the D and B channels in a D, D and B, or D and 2B bearerchannel configuration as needed and tearing them down when they areidle. The ISDN D channel carries control messaging and cannot be torndown while the ISDN call is still active. Accordingly, dynamic bandwidthallocation for ISDN service only relates to the addition and tearingdown of B channels.

The procedure 400 for dynamic allocation of bandwidth for ISDN servicein accordance with the present invention will be explained in greaterdetail with reference to FIG. 5. When an ISDN call is initiated, the Dchannel is established first (step 402). The bandwidth required for theparticular application is communicated from the calling ISDN equipmentto the called ISDN equipment through messages on the D channel (step404). These messages are in HDLC format and the RCS 104 monitors thesemessages via an HDLC interface (step 406). Once the RCS 104 determineshow many B channels are required (step 408) it initiates establishmentof these bearer channels over the air interface (step 410). The RCScontinues monitoring the HDLC messages on the D channel during the ISDNcall (step 412) and determines if additional B channels are to beswitched in or out. In case that additional B channels should beswitched in or out, the RCS 104 initiates the establishment or tearingdown of the bearer channels over the air interface (step 414).

A flow diagram showing simplified procedure 600 of the bearer channelestablishment will be described with reference to FIGS. 6A and 6B. Thesubscriber unit 111 quickly ramps up its transmit power (step 602) whilesending the SAXPT (step 604). When the RCS 104 detects the SAXPT (step606), it turns the traffic light bit to “red” on the FBCCH (step 608) tosignal to the subscriber unit 111 that it has been detected. The RCS 104transmits the FBCCH (step 610). The subscriber unit 111 monitors theFBCCH (step 612) and it stops the fast ramp-up when it sees the “trafficlight” turn red on the FBCCH (step 614). The subscriber unit 111 thencontinues a slow ramp-up of its transmit power (step 616) whiletransmitting the LAXPT (step 618). When the RCS 104 acquires the LAXPT(step 620), it informs the subscriber unit 111 via the SYNC-OK messageon CTCH (step 622). This completes the transmit power ramping up part ofthe access procedure.

After the subscriber unit 111 receives the SYNC-OK message on the CTCH(step 624), it sends the access request message on the AXCH (step 626).Upon receiving the request (step 628) the RCS 104 confirms receipt ofthe AXCH message with a message on CTCH (step 630), which includes theassigned code seed. The subscriber unit 111 detects and acknowledges thebearer confirmation message that carries the assigned code seed on theAXCH (steps 632 and 634), which the RCS 104 detects (step 636). The codeswitchover is now negotiated and subscriber unit 111 and RCS 104simultaneously switch to using the assigned code (steps 638 and 640).The bearer channel is now established.

The layered protocol of the communications between the subscriber unit111 and the RCS 104 is shown in FIG. 7 along with its correspondence tothe layers of the Open Systems Interconnection (OSI) reference model.The physical (PHL) layer performs the following functions: 1) generationof CDMA codes; 2) synchronization between transmitter and receiver; 3)providing bearers to the Medium Access Control (MAC) layer; 4) spreadingand transmission of bits on a CDMA code specified by the MAC and at apower level specified by the MAC; 5) measurement of received signalstrength to allow automatic power control; and 6) generation andtransmission of pilot signals. The MAC layers performs the followingfunctions: 1) encoding and decoding for forward error correction (FEC);2) assignment of CDMA codes; 3) encryption and decryption; 4) providingbearers which are encrypted and error-corrected as appropriate; 5)framing, error checking and discrimination of MAC peer to peer messagesand data; 6) link control (DLC) frames; and 7) processing of automaticpower control information. The data link control layer (DLC) provides anerror-free link between higher level layers of the protocol stack.

As shown in FIG. 8A, the signaling between the subscriber unit 111 andthe RCS 104 involves the MAC and DLC layers of the protocol. Once thebearer channel for POTS service is established as described above, theservice is available and remains unchanged until it is torn down orunless it has to be modified to support a facsimile transmission or asecond call, in the case of a simultaneous OA&M call and POTS call. Whenthere is an OA&M call in progress and the subscriber unit 111 initiatesa POTS service call, the procedure as shown in FIG. 8A is entered. Thisfigure illustrates the simplified bearer switching method as initiatedby the subscriber unit 111. The messages go between the data linkcontrol layer (DLC), medium access control layer (MAC) of the subscriberunit 111, and the corresponding layers in the RCS 104. First, the DLClayer of the subscriber unit 111 initiates a switch request to the MAClayer of the subscriber unit 111, which refers this switch request tothe MAC layer of the RCS 104. The RCS 104 sends a confirmation over theMAC layer to the subscriber unit 111 and also sends a switch indicationto the DLC layer of the RCS 104. In the subscriber unit 111, the switchconfirmation sent from the RCS 104 over the MAC layer is forwarded tothe DLC layer of the subscriber unit 111.

When there is a POTS service call in progress and the RCS 104 initiatesan OA&M call to the same subscriber unit 111, the procedure as shown inFIG. 8B is entered. This figure illustrates the simplified bearerswitching method as initiated by the RCS 104. The RCS 104 initiates aswitch indication message over the MAC layer to the subscriber unit 111.The subscriber unit 111 then relays this message via the DLC layer.

The bearer channel establishment for ISDN will be explained withreference to FIGS. 9A and 9B. Steps 902-940 are the same as thecorresponding steps 602-640 in FIGS. 6A and 6B. However, severaladditional steps are required after the subscriber unit 111 and the RCS104 both switch to the assigned codes (steps 938 and 940). Once thesubscriber unit 111 and RCS 104 switch to assigned codes (steps 938 and940) the ISDN D channel becomes active. At this point the S/T interfacebetween the subscriber unit 111 and the ISDN equipment is alreadyactive. The RCS 104 starts monitoring the D channel messages (step 942),which are in HDLC format. Upon detecting that one or more B channels areneeded for the particular application (step 944) the RCS 104 initiatesestablishment of these bearer channels over the air interface. Theprocess is then continued in accordance with the procedure shown in FIG.5. The MAC and DLC message flow for this procedure is the same as inFIG. 8B.

The bearer channels for POTS and ISDN is switched in or out via the samemessage flow. Whether the bearer channel is switched in or out isindicated by appropriate values in corresponding fields of the D channelmessages. Therefore the flow diagram in FIG. 8B apply to both dynamicswitching in of bearer channels as well as dynamic switching out ofbearer channels.

Although the invention has been described in part by making detailedreference to certain specific embodiments, such details is intended tobe instructive rather than restrictive. It will be appreciated by thoseskilled in the art that many variations may be made in the structure andmode of operation without departing from the spirit and scope of theinvention as disclosed in the teachings herein.

Hereafter, a wireless transmit/receive unit (WTRU) includes but is notlimited to a user equipment, mobile station, fixed or mobile subscriberunit, pager, or any other type of device capable of operating in awireless environment. When referred to hereafter, a base stationincludes but is not limited to a Node-B, site controller, access pointor any other type of interfacing device in a wireless environment.

1. A code division multiple access (CDMA) subscriber unit comprising: anantenna; and a circuit coupled to the antenna, the circuit beingconfigured to provide a first signal to the antenna which iscommunicated to a base station over a first channel at a first datarate, the circuit being configured to generate a second signal which iscommunicated to the base station, wherein, in response to the secondsignal, a second channel is established between the CDMA subscriber unitand the base station, the circuit being configured to provide a thirdsignal to the antenna which is communicated to the base station over thesecond channel at a second data rate different than the first data rate,wherein the circuit is further configured to receive two callssimultaneously; wherein the antenna is configured to receive powercontrol information which is time division multiplexed onto a physicalchannel with signaling information, the circuit being configured toadjust a power level associated with at least one of the first andsecond channels in accordance with the power control information.
 2. TheCDMA subscriber unit of claim 1, further including a digital signalprocessor.
 3. The CDMA subscriber unit of claim 1, further including aCODEC circuit.
 4. The CDMA subscriber unit of claim 2, further includinga filter circuit.
 5. A method for use in a code division multiple access(CDMA) subscriber unit, the method comprising: transmitting a firstsignal to a base station over a first channel at a first data rate;generating a second signal, wherein, in response to the second signal, asecond channel is established between the CDMA subscriber unit and thebase station; transmitting a third signal to the base station over thesecond channel at a second data rate different than the first data rate;receiving two calls simultaneously and power control information whichis time division multiplexed onto a physical channel with signalinginformation; and adjusting a power level associated with at least one ofthe first and second channels in accordance with the power controlinformation.